The invention generally relates to printing presses and, more particularly, relates to scraping or doctor blades for use with printing presses.
Keyless printing presses commonly employ a series of rollers, referred to as an ink train, to direct ink from an ink source to a cylinder which applies the ink to a moving web of paper. The series of rollers comprising the ink train, and communicating the ink to the web of paper, accurately meter the ink to ensure that the appropriate amount of ink is transferred to result in an accurate and aesthetically pleasing appearance in the printed text or image.
One additional device used to meter the amount of ink transferred to the paper is referred to as a scraping or doctor blade. The blade includes a tip in direct contact with a scraper roller of the ink train to scrape excess ink from the scraper roller. The removed ink is typically directed via gravity into an ink module provided directly below the blade. The removed ink is then recycled back to an applicator device at the beginning of the ink train for ultimate re-application to the web.
One difficulty associated with known scraping blades is that both the ink and the roller against which the blade scrapes are abrasive. The material from which the blade is made therefore tends to wear, resulting in a relatively short serviceable life, sometimes as short as forty hours of use. This in turn results in longer downtime for the press, and ultimately in added expense to the operator.
An additional factor complicating the situation is that the blade must be deflectable or deformable to ensure the blade maintains contact with the roller throughout its operation. The blade is typically mounted at an angle to the circumferential surface of the ink roller and is mechanically or otherwise biased toward the roller to ensure such contact. In light of such a requirement, the blade typically cannot be manufactured from extremely high hardness or wear resistance materials as such materials typically do not afford the necessary deflection characteristics needed in the blade.
Moreover, with known blades the material of the blade can be worn away so quickly, that the air cylinder or similar device biasing the blade toward the scraping roller can push the blade to such a steep angle with respect to the roller circumference that the blade tends to plow the ink, rather than remove the ink.
The prior art has provided a number of different types of doctor blades. For example, U.S. Pat. No. 5,638,751, discloses a doctor blade of a stepped construction. More specifically, the doctor blade includes a thin tip portion which transitions into a thicker doctor blade portion, which in turn transitions into a thicker backup or base portion. The variable thicknesses ensure the necessary deflection characteristics in the blade, while the thicker backup portion provides adequate structurally rigidity. However, the thin tip portion is the section of the blade that actually engages the ink roller and, given its thin dimension, wears away relatively quickly.
In accordance with one aspect of the invention, a printing press ink scraping blade is provided which comprises a base end adapted to be mounted to a printing press, and a working end extending from the base end. The working end includes a scraping tip for engagement with an ink roller. The working end is unitary with the base end and has a thickness greater than the base end.
In accordance with another aspect of the invention, a method of fabricating a printing press ink scraping blade is provided which comprises the steps of forming a blank from the deflectable material, creating a bevel into a working end of the blank, and removing material from a base end of the blade to create a unitary scraping blade having a thicker working end than base end.
In accordance with another aspect of the invention, a printing press is provided which comprises a frame adapted to carry a web of paper through the printing press, at least one cylinder adapted to imprint ink on the web, an ink train adapted to carry ink to the at least one cylinder, a scraping roller, and a scraping blade in contact with the scraping roller. The scraping blade has a working end and a base end. The working end is integral with, and thicker than, the base end.
In accordance with yet another aspect of the invention, an ink scraping blade is provided which comprises a back edge, a front edge, first and second side edges, a bottom surface, and a top surface. The front edge is beveled. The bottom surface is substantially planar. The top surface includes a working end portion proximate the front edge and a mounting end portion proximate the back edge. First and second side edges are thicker adjacent the working end portion than adjacent the mounting end portion. The ink scraping blade is manufactured from a unitary piece of material.
These and other aspects and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.